Island



UNITED STATES ATENT FFICE SAMUEL POXVEL, OF NEIVPORT, RHODE ISLAND, ASSIGNOR TO HARFORD WILLING HARE POVVEL, TRUSTEE.

PROCESS OF MAKING IRON PICTURES.

SPECIFICATION forming part of Letters Patent No. 337,703, dated March 9, 1886.

Application filed November 2, 1883.

To all whom it may concern.-

Be it known that I, SAMUEL PowEL, a citizen of the United States, residing at Newport, in the county of Newport and State of Rhode Island, have invented certain new and useful Improvements in the Process of Photography for Making Iron Pictures or Blue Prints and of Modifying Them; and I do hereby declare that the following is a full, clear, and exact description of the invention, which will enable others skilled in the art to which it belongs to make and use the same.

The object of my invention is the production of a permanent picture or print in satisfactory resultant colors, with a preservation of delicacy in the gradations or half-tones and a purity of whites; and to this end myinvention consists in materially altering and removing the objectionable color of iron pictures or blue prints, and making or converting them into black, dark, or other desirable tints or colors.

To carry my invention into effect, first, the paper is prepared in the dark with a compound of iron sensitive to light; second, it is duly exposed under a negative to the action of light; third, it is developed by duly washing several times in changes of clean water and dried. This is the cyanotype picture or blue print. To change the color, I must discharge the strong blue color by means of a discolorizing bath, and on removing from the discolorizing or discharging bath the new color is to be produced by treatment with proper reagents, which are numerous. Any good hard wellsized paper is usually employed for the cyanotype picture; but to produce modified colors with pure shadows, tints, and whites, I pass such paper first through a bath of dilute gelatine, which had better contain two and a quarter (25) grains of gelatine for each ounce of water. Then, after passing the paper through the gelatine-bath, it is hung up to drain and dry, using all precautions to avoid unevenness of coat, streaks, and marks. When quite dry, this sized paper should in the dark be very evenly coated with a solution composed of, say, seventy grains of ammonia-citrate of iron with sixty (60) grains of ferrid-cyanide of potash in two (2) ounces of wa- Serial No. 110,700. (No specimens.)

ter, which should be prepared andhept in the dark. This is the prepared paper which, when duly exposed under a negative to light, may produce the variety of image desired. lVhen printed,it is washed in two (2) or three (3) changes of clean water, and I have the developed print no longer sensitive to light. This print needs now only to be blotted off from superfluous water, when it is ready for immersion in the discharging or decolorizing bath.

The dischargi ng-bath I have discovered may be composed of a variety of agents, such as, (a,) the carbonate, bicarbonate, or sesquicarbonate of soda; (b,) the soluble alkaline silicates of potash and soda; (0,) biborate of soda, known as borax.

Any of the above reagents dissolved in the proportion of about ten (10) grains to the ounce of water will discharge the color of the blue prints, still leaving the salt of iron in the form of a nearly invisible and perfect image in the paper.

I prefer to compose the discharging-bath of, say, ten (10) grains of effiorescent sesquicarbonate of soda with each ounce of water. In this bath I immerse the blue print till the color is discharged and the paper loses nearly all trace of the picture, except a rusty color more or less distinctly marked with theimage in the strong shadows. WVhen the blue color has vanished in the dischargingbath, the paper is washed two (2) or three (3) times in changes of clean water, and is then blotted OK to remove any remaining traces of soda-salts, which, if left in the print, would modify the final color. The print is now discharged and ready for the coloring-bath, for which we may employ gallic acid, tannin, pyrogallic acid, and all other suitable compounds of tannin, and such other agents as are known and employed to produce colored reactions with salts of iron, and of which I now prepare a coloring-bath, as, say, of four (4) grains of gallic acid to the ounce of water, in which 1 immerse the print and, then watch carefully for the development of the desired color,

which, when it appears, is the signal to re-- move the print from the coloring-bath, and to pass it once rapidly through one bath of clean water, so as to fairly wash it, then immediately to blot it ofi until it has given up all the superfluous water, and finally, it is strengthened and rendered much more brilliant by drying in the full daylight, and, preferably, even in sunlight.

By the old method, when an alcoholic solution of caustic potash was applied to the prints, a blurring effect was liable to be produced; but by my process the agents employed, as above described, and especially with the gelatine-sized paper, are essential means of producing reactions that leave in the print an insoluble salt or salts, so that in the final process there is no tendency to blur.

A further striking advantage of my process is that it produces a picture or print highly I insensitive to the fading action of light.

The method of transforming the color ofcyanotypes or blue prints into any other than the ing, subsequently recoloring it by the appli cation of the hereinbefore-described recoloring-bath (gallic acid) in or about the proportion hereinbefore set forth, substantially as described.

July 7, 1883.

SAMUEL POWEL.

Witnesses:

JOHN HARE PowEL, J r., MARY EDITH PowEL. 

